In Windows there are a number of tweaks that can be made to improve the performance of the PC. Some of them are widely known, such as deleting temporary files, defragmenting the hard drive, turning off background programs; others are less well known, such as switching off unnecessary services, or cleaning up registry errors. This piece of software does the lot, and it does it very efficiently with a great balance between flexible options and straightforward user-friendliness.
The first thing I must say is that maintaining your PC's health using these sorts of tools will not speed up your computer very much. It's certainly not going to make you think hey, my slow computer is now flowing as freely as the day it was bought! But that's not what it's supposed to do, performance and health is not the same as speed. What this is product is great for, is keeping everything nicely organised, and making sure all the minor errors don't stack up and make things freeze up.
It's worth mentioning that nearly all of the features are already available on Windows, but many of them (such as changing the status of all those unnecessary background services that are running) are time-consuming and have to be done one by one. Performance Toolkit 2011 doesn't do anything magical that you couldn't do yourself if you could be bothered to go through it all manually, but it brings everything together and lets you do it all in one go.
One essential feature for me is that everything can be restored. So if you run the registry cleaner and afterwards things seem to be even worse, you can easily revert to how it was beforehand. Another essential feature is that the program (almost) always tells you exactly what it's going to do and lets you choose to exclude or include certain categories should you wish to. So with the clean up function maybe you want to delete your internet history but keep the contents of the recycle bin, you can do that, or if you just want rid of everything you can easily do that too.
One feature that is particularly of note is the ability to recover or bleach deleted information. When you delete something from your computer, it doesn't just disappear from your hard drive, but the space it occupies is made available for something else. Only when that space has been extensively written over with something else will the original information be erased. Performance Toolkit 2011 can both recover some of this information that has not been overwritten and can bleach it, making it completely unrecoverable. (Bear in mind that a lot of deleted files will have already been written over so many times that they are irretrievable no matter what.)
So what are the downsides? Well, if you're fussy about precise tinkering with your computer, maybe you want something with a few more options. And if you're expecting this to cure a broken computer, it probably won't, in the same way that cleaning your car, changing the tyres, topping up the oil, etc, won't make your car run if the engine is broken. There were two small things that annoyed me, one being an optimize button that didn't actually tell you at any point what it was optimizing or how, and the other being the health status meter, which is actually just a how-long-since-you-last-used-me meter.
Overall, it's a great thing to have, and I'll certainly continue to use it. I wouldn't go as far as to call it essential, you can do most of the things it does anyway if you've got the time and will power to do it with Windows, but it certainly makes all PC maintenance issues much, much easier to stay on top of. If you're just looking for something to fix your computer, be warned, it will probably help a bit, but it's not going to wave a magic wand and cure it all.